1. Field of the Invention
The present invention relates to an apparatus for filling a liquid or highly viscous material into containers. More particularly, the invention concerns an apparatus capable of filling into containers, in a stable and continuous manner, a liquid or highly viscous product containing solid matter after treatment under a high pressure, while avoiding application of the high pressure to any part of the filler means. The invention is also concerned with a sterilizer making use of the filling apparatus.
2. Description of the Prior Art
In the fields of foodstuffs or medicines, it is a common measure to sterilize the products, before the products are sold commercially, to a state in which the products are amicobiologically safe, in order to prevent any putrefaction of the product by microorganisms during storage. The sterilization of the foodstuffs and medicines is preferably performed at a high temperature in a short period of time, in order to avoid any degradation of the quality which may occur during the sterilizing treatment.
When the sterilization of the product is performed at a high temperature exceeding 100.degree. C., the product will be unfavourably boiled in the sterilization system if the treatment pressure is maintained at the normal level. In order to avoid such boiling, hitherto, it has been necessary to maintain a predetermined boil-suppressing pressure (referred to as "back pressure" hereinunder) within the sterilizing system. This conventional sterilizing method, however, has suffered from the following problems.
Namely, in one of the known sterilizing systems, two pumps are arranged upstream and downstream of the sterilizer as viewed in the direction of flow of the material under treatment, and the back pressure was obtained by suitably controlling the discharge rates of two pumps. In this system, however, the pump downstream of the sterilizer is subjected to a considerably high temperature or pressure if the sterilization temperature is raised to 120.degree. to 150.degree. C. which ensures a biologically safe sterilization. Consequently, a leak takes place in this pump to unstabilize the flow rate and pressure of the product in the sterilizer, resulting in a fluctuation of the treating condition.
Another known method for obtaining the back pressure employs a pressure control valve or a homogenizer in place of the downstream pump. In this case, if the product contains solid matter, the pressure control valve or the homogenizer tends to be clogged with this solid matter which would incur an extraordinary pressure rise in the system.
A sterilizing system suitable for the treatment of material containing solid matter and, hence, free from the problem of clogging is disclosed in a German magazine "Die Molkeri-Zeitung Welt der Milch, 35. Jahrgang, 1981/41). This system has a pressure feeding pump at the upstream side of the sterilizer and a back pressure tank disposed at the downstream side of the same. The back pressure tank has a controllable pneumatic pressure by which the back pressure is applied to the sterilizer. With this system, therefore, it is possible to treat the material containing solid matter in the sterilizer at a constant high temperature under a stable back pressure. In addition, the problem concerning clogging can be avoided because there are no parts such as a pressure control valve or homogenizer which would be clogged with the solid matter.
The sterilization system shown in the above-mentioned magazine fully shows its merit particularly when the same is used in the sterlization of the material containing solid matter. In this sterilizing system, however, the following problem is encountered when a filling machine is connected to the downstream side of the back pressure tank because the same pressure as that acting in the sterilizer is applied also to the portion of the system downstream from the back pressure tank.
In general, the parts constituting the filling machine connected to the sterilizing system can withstand only comparatively low pressure so that the application of the same pressure as in the sterilizer to these parts of the filling machine is preferably avoided from the view point of mechanical engineering. The application of such pressure causes also various problems such as a fluctuation of the filling amount, "liquid dripping" due to leaking of the liquid product from the filling valve due to high pressure, and a splashing of the product resulting in a phenomenon called flushing when the filling valve is opened.
In this sterilizing system, therefore, a valve or a suitable means is disposed to selectively disconnect the filling machine from the sterilizer and the back pressure tank downstream from the sterilizer. In operation, the valve is closed to disconnect the filling machine during the sterilization and the sterilized product is temporarily collected in the back pressure tank without decreasing the pressure. Then, after stopping the operation of the sterilizer and dropping the pressure in the system portion including the back pressure tank, the valve is opened to allow the product to be fed to the filling machine. In this case, however, the sterilization and the filling have to be conducted in separate steps, which is quite inconvenient from the view point of continuous processing of the product.
In still another method, the pressure control valve or the product transferring pump is disposed between the back pressure tank in the sterilizing system and the filling machine. In this method, therefore, normal pressure is maintained in the system downstream from the pressure control valve or the pump, so that the filling machine is kept away from the pressure acting in the sterilizer. The use of the pressure control valve, however, tends to cause an abnormal pressure rise in the system due to clogging of the pressure control valve with any solid matter which may be contained in the product, often resulting in a breakdown of the sterilizing system. The containment of solid matter is permissible to some extent provided that the pump is used instead of the pressure control valve. In such a case, the solid matter is made to pass through various clearances existing in the pump, so that the solid matter is broken up. Thus, this method cannot be used suitable for products containing solid matter of large size.
Accordingly, the present invention intends as its primary object to provide a filling apparatus which is free from the problems of the prior art explained hereinbefore.
More specifically, it is a main object of the invention to provide a filling apparatus for filling into containers a liquid or highly viscous products treated at a high temperature and pressure to permit the filling of the product while avoiding the application of the high treating pressure to the parts of the filling machine.
Another object of the invention is to provide a filling apparatus which, when incorporated in a sterilizing system, permits a continuous high-temperature sterilization under a constant back pressure while avoiding application of excessive pressure to the parts of the filling machine, thereby to ensure a continuous and stable sterilization and filling.
A further object of the invention is to provide a filling apparatus which is improved to permit treatment of products even when the latter contain solid matter of comparatively large size.
These objects of the invention are achieved by providing a process comprising the steps of: (1) treating the product under a high pressure and collecting the same in a pressurizing tank without decreasing the pressure, (2) transferring the product from the pressurizing tank into a buffer tank which is connected to the downstream side of the pressurizing tank, while maintaining the pressure in the buffer tank at a level the same as or slightly below the pressure in the pressurizing tank; (3) bringing, after disconnecting the buffer tank from the pressurizing tank and decreasing the pressure in the buffer tank, the buffer tank into communication with a filling tank downstream of the buffer tank and having beforehand a low internal pressure, thereby to transfer the product from the buffer tank to the filling tank; and (4) transferring the product to the filling machine through the steps of (1) to (3) above. With this process, it is possible to treat the product continuously under high pressure and collect it by a pressurizing tank without suspending the operation. In addition, by repetitiously taking the steps (2) to (4), it is possible to conduct a stable and continuous filling of the product without subjecting the filling machine to a severe pressure condition.
The present inventors also worked out a sterilizing system having, at the upstream side of the filling apparatus, a sterilizer and a feeding tank or a feeding pump for supplying the sterilizer with the product, and a pressurizing tank downstream from the sterilizer, the pressurizing tank having a controllable pneumatic internal pressure for applying the back pressure to the sterilizer. According to this arrangement, it is possible to stably and accurately control the back pressure because the back pressure is transmitted through the medium of the air. With this system, therefore, the products are sterilized under quite a stable condition. This advantage, in combination with the aforementioned stable and continuous filling operation of the filling apparatus, offers an extremely superior performance of the sterilizing filling apparatus.
The present invention also provides a filling apparatus comprising: a pressurizing tank; a buffer tank; filling tank; and a filling machine; the tanks having independently controllable internal pneumatic pressure, and being connected in series by transfer pipes having valve means.